1. Field of the Invention
The present invention relates to a numerical controller and, more particularly, to a numerical controller capable of machining condition control based on the posture of a nozzle which a laser beam machine includes.
2. Description of the Related Art
Three-dimensional laser beam machining includes machining along a curved workpiece surface and machining (bevel cutting) with a nozzle inclined with respect to a workpiece.
In the case of machining along a curved workpiece surface in three-dimensional laser beam machining, even if machining is performed such that a nozzle center point (tool center point) is at a constant speed, a corner portion or the like has a difference in machining speed between a workpiece upper surface and a workpiece lower surface. For example, assume a case where the N1 to N3 blocks are machined under the same machining condition at the time of machining along a curved surface of a workpiece, as in FIG. 11. Since a travel amount L2 of an extended tool center point (to be described later) at a lower surface of a workpiece 2 at the time of machining of the N2 block in FIG. 11 is smaller than a travel amount L1 of a tool center point at an upper surface of the workpiece 2, the machining speed at the lower surface of the workpiece 2 is lower than that at the upper surface of the workpiece 2. This may cause poor machining at the lower surface of the workpiece 2.
In the case of bevel cutting, since machining is performed with the nozzle 1 inclined with respect to the workpiece 2, a board thickness at a portion to be machined is a board thickness D2 different from a board thickness D1 when the nozzle 1 is perpendicular to the workpiece 2, as shown in FIG. 12. Thus, a machining condition needs to be changed from a machining condition when the nozzle 1 is perpendicular in accordance with an inclination angle of the nozzle 1.
When circular interpolation is performed in bevel cutting, as shown in FIG. 13, a travel amount L2 of an extended tool center point at a lower surface of the workpiece 2 is larger than a travel amount L1 of the tool center point at an upper surface of the workpiece 2, and the machining speed at the lower surface of the workpiece 2 is higher. In this case, a machining path is common to both a case where the nozzle 1 is perpendicular to the workpiece 2 and a case where the nozzle 1 is inclined with respect to the workpiece 2. At the time of program creation, however, a machining condition different from a machining condition when the nozzle 1 is perpendicular to the workpiece 2 needs to be specified in consideration of the tilt of the nozzle 1 with respect to the upper surface of the workpiece 2.
Note that a technique for changing a machining condition in accordance with the speed of a nozzle tip (for example, Japanese Patent Application Laid-Open No. 09-150282 or Japanese Patent Application Laid-Open No. 2000-351087) and a technique for creating a machining program including machining condition data from a machining shape (for example, Japanese Patent Application Laid-Open No. 06-110524 or Japanese Patent Application Laid-Open No. 06-142954) are publicly known as prior art techniques pertaining to change of a machining condition.
In the techniques disclosed in Japanese Patent Application Laid-Open No. 09-150282 and Japanese Patent Application Laid-Open No. 2000-351087 described earlier, however, no regard is given to a shape at a workpiece lower surface. To prevent poor machining in the case of machining shown in FIG. 11, separate machining conditions need to be purposely specified for a linear portion (the N1 or N3 block) and a corner portion (the N2 block) at the time of program creation. For example, when three-dimensional machining is performed such that the nozzle 1 is always perpendicular to the workpiece 2, as in FIG. 11, since the N2 block corresponds to a corner, a machining program which specifies a machining condition different from a machining condition for the N1 and N3 blocks needs to be created.
Even if the technique disclosed in Japanese Patent Application Laid-Open No. 06-110524 or Japanese Patent Application Laid-Open No. 06-142954 is used, an NC program which specifies a detailed machining condition in accordance with a machining shape needs to be created in advance on the basis of information, such as CAD/CAM data, which is troublesome. For example, to perform linear machining with the nozzle 1 perpendicular to the workpiece 2 for the N1 block, linear bevel cutting with the nozzle 1 tilted at an angle θ with respect to the workpiece 2 for the N2 block, and circular bevel cutting with the nozzle 1 tilted at the angle θ with respect to the workpiece 2 for the N3 block, as in FIG. 14, a machining program which specifies different machining conditions for the N1, N2, and N3 blocks needs to be created.